----------------------------Original message---------------------------- The 15 minute topographic sheets are one of the most valuable series of maps that any map collection could possess in my mind. They have saved for posterity the location of small villages, railroads, cemeteries, old schoolhouses, and many other physical and cultural features that I have used them for. The Harvard Map Collection's set has been "locked up" for some time, however, this fall we will be deacidifying the New England collection. They are probably as valuable as those "old" nautical charts and "old" Sanborn maps! David A. Cobb Harvard Map Collection